Electronic organ



D ec- 26 1950 A. M. SKELLETT 2,535,323

ELECTRONIC oRGAN F/L TE l? 11\I VEN TOR. ALBERT M f/(EZLE 7'7" l ain/5y Dec. 26, 1950 l A. M. SKELLETT ELECTRONIC ORGN 2 Sheets-Sheet 2 l Filed Jpne 9, 1949 INVENTOR. M55/P7' M. .SNEL/.Err BY hv .m @E

A Tra/PN? EY ization ofj 'el Patented ec. 26, 1950 En fis PATENT :oF-n CE f E'Ihre'TRONIC-f'cR`f(i1l.i\

:i2-.Albert #Miff-Skellett,l f'MadisonV-N. J., assigner .to .,{National VUnion Radio f-Corporation, .rOrange,

N. J.; .a .conporatonof Delaware fi Allicati 3111169, 1949, Serial N 015975953 combinations Thepresentinventienhasfforfone of it 'prinipalbbje'otsffthe 'provision ofwan elec- 'intervening'fe eetrodes;"vfitl-assoeiatedeaudio'-A re- Affurtlfrer featurefrelatesllto tnefnevel organ-ilo tub ndr-associated'oscillatory turesft-herewith.

-appendedfelaims- Irlthe'- "drawing, Figi v.lfiis-a 'fcompositevs'chematic vstructural 'zand "wiringl diaraml ofl'aln electronic forgarri-Lfaccord- .ing tfthefinventin.

42;:3r and-141are?respective?modicationsrof i2 Referring lto:Fig. 1, the' numeral l "represents :anlele'ctronic-ftube structure of the type disclosed in my. prior-Patent No.'2,433-,403 andwn vthelPro- 'ceedingsof f the `Institute of Radio VEngineers',Mol. 36, No. 11, pages 135424357. This tube-comprises an evacuated enclosing. glass; envelope 12,; having centrallylfmounted there-innen electroneemitting cathoder. f This` 'cathodeifisfpreferably:fofrtnefin Idirectly heated type comprising la ftubulartrietal sleeveft'he :external .fsur-faicezrrof lwhich is coated with -felectron'emssive w.:materia1. .nsulatngly mounted :WithinA the sleeve- Suis. a heat'erselement 3a for raising. the `c'zatllcde to its "electron .emission temperature. Concent-rcally z surrounding 'the cathode 3 is arcyi -dricalfmetalcagefconsistingauf alternate .slats-W :and 'interveningawindowsr Concentrically surrounding the-,cathode 3 andn alignrnent with seachi ofhthefrespect-vei Windows, -isA afseries "of f'forannoust'electrodesfor sgrdsfv. Likewise,vr Goneent'rical'ly surroundii-iglt'hel cathode, and infalignmentwith the gridsf, farerthendi'- vidual output ano'des 1. -The'cathodeS-Jray 'be `directly groundedforexample: by'f thexconductor 8, and .thefcagerl of which the shield. islats" l are .constituted"carifbelconnected-zb onductor'to vafsuitalole :tap'iflO-fonthe. usua irectfcurrent .power supply. In accordancef-vJithf-:one-phasnf the. invention", this: latter :circuit includes a :series resistor.'1lbforexamplefrofzapproximately :103000 ohms forfpurposes` to'be. described. r

.-In accordanceJ `Witlrthe inventions-sarah@ set of electrodesd, andi-1;'cooperates withlthezeommon "catlgtlo'def tergenerateza. respective sustainedeelecztrical ozscilationnffr predetermined respectivexed frequency. Thus, Aeac-lrfof these individualxsections ris connedtedto-atuned oscillatory'circuiti-to .generate its vrespective :tonal lfrequencmethejfproduction of/fwhiclrlcan be .controlled by; aw'corresponding'- key; for Gexampleifltewl 2 of =tl1e usual organfkeyboard..fEachfof: these keys iseassociated with. anA individual; -mova-ble'contact l Seand a cofo-peratingfncommonlcontactfstip:lil which is con- .n-eetedz-to e suitable :high pOtentiar-tap 'Ii-ofnfthe direct current; power? supply source-l Thefmov- .able contact. .-associate'dliwtin'- ea'chwley,l fior exiample'lthe "contactwlafrf-s connectedlby c'onductor v.I1 tothe 'electrical midpointV :18 Ourthe-primary -winding- :l 9 .for-Fan audio-:frequency "transformer A2l). One ABterminalf ofi the f --Izairnairy` iwind-i'ng, :for

.examplefterminal' 21| ',sisconnectedvdirectly' to: the ,associatedvanode ,'Lj. ands the oppositefzterminal i2 2 is: connected. throughta f1direct-=f current blocking condenser-:23110 the' corresponding-.grid :6. @Each #grid v6 fs-rfw'connectedfto1 a 'irrespective 'egridleak `resistor 242.1to-thconimonfmuitiplyingneonductor 25 which can be returned to ground through a suitable normally-closed switch 26. The winding I9 is shunted by a condenser 21 to form therewith a tuned oscillatory circuit. It will be understood, of course, that each set of electrodes of tube I has a similar audio frequency transforme-r and tuning condenser conne-cted to its respective anode and grid, and each of these circuits is tuned to a different fundamental frequency corresponding to the fundamental tones to be produced. When the various electrodes are energized by suitable potentials as above mentioned, a portion of the primary winding I3 is connected between the grid and cathode of the corresponding tube section, and the remaining portion of this primary winding is connected between the anode and cathode of the same section. Thus, by well-known regenerative feedback principles, each section generates a corresponding audio frequency electric wave. All the secondary windings 28 of the audio frequency transformers are connected in series across the output conductors 29, 30, which are connected to a suitable audio frequency amplifier 3|, and thence to a suitable loudspeaker r reproducer 32.

With the foregoing described arrangement, it is possible to produce an individual tone, or simultaneously a series of pure fundamental sustained tones, representing chords. I have found that it is possible to combine with these fundamental frequencies any desired harmonics, by tapping-off from the slat electrodes 4 at the common point 33 through a direct current blockm ing condenser 33a, a series of filters 34, 35, 36, each of which can be designed to pass a selected harmonic lor group'of harmonics of the fundamental frequencies appearing at conductors 29, 30. These filters can be controlled by respective stops 31 to determine the desired selection of harmonics to be mixed with the fundamental tones applied to the input of amplifier 3|. For this purpose, each of the filters 34, 35, 35, is connected to an individual movable contact 38 controlled by a respective stop 31, and cooperating with a common contact strip 39 which is connected to the input terminals of a suitable mixer network 40. The output terminals of the mixer 40 are then applied to the amplier 3|, thus producing in the loudspeaker any desired fundamental and harmonic content.

In the event that a. tremolo effect is to be imparted to the various notes or chords, there is provided a tremolo mechanism consisting of a crank wheel 4| which is connected through suitable gears 42 to a motor 43 so as to drive the wheel 4| at a predetermined rate, for example seven revolutions per second. The eccentric or crank arm 44 of the wheel is connected to a rotatable arm 45 which is adapted to ride over a potentiometer resistor 46. Bridged across the resistor 46 is a suitable source of direct current potential 41,' the positive terminal of which is grounded. VThe arm 45 is also connected to a contact 48 of atremolo switch 49, the armature 50 of which is connected to conductor 25. The other contact of switch 49 is connected to the negative terminal of a, suitable direct current source 52. When the trexnolo efectis desired, the arm 5|) is moved to engage ment with contact 48. Since the arm 45 is continuously moving back and forth across the resistor 46 at a rate determined by the wheel 4|, there is thus supplied to the conductor 25 a trembling or varying negative bias which is thus applied to all the grids 3. When the tremolo potential, for example 150 volts, to the correspending anode 1. This produces a somewhat percussive organ tone or sharp attack. If it is desired to slow-down the attack on the immediate generation of the tone, so as to smooth its percussive effect, a separate normally-closed tonal attack key or stop 43 can be opened to connect in series with the keys, a suitable timeconstant circuit constituted of resistor 44 and shunt condenser 45. With the described arrangement, by tapping-off the lters 34, 35, 36, from the slat electrodes 4, the voltage drops developed across resistor |I by the operation of any of the stops 31, may be used as a source of harmonics which can be mixed with the fundamental tones of the respective individual keys I2 to produce the various kinds of organ tones, such as diapason, flute, oboe, vox humana, etc.

While the drawing shows a tube consisting of twelve individual tone-producing sections, it has been found possible to manufacture tubes of this type with thirty such sections. Since a two-manual organ contains about one hundred and thirty-two keys with twenty-five or thirtytwo extra tones for the foot pedals, it is possible, according to the invention, to produce a complete two-manual organ employing only ve or six tubes such as tube I.

In some cases it may be desirable to segregate the various harmonics produced atY the several slat electrodes 4. In the arrangement of Fig. 1, all the slat electrodes are interconnected to form a single electrical cage. However, instead of using a single cage, the various slats 4 can 1, be insulated from each other and provided with separate lead-in conductors,`and through their respective resistors thus rendering it possible to segregate the various harmonics as may be desired. Such an arrangement is schematically illustrated in Fig. 2 of the drawing. Merely for simplicity of showing, Fig. 2 illustrates only two of the several sections of the tube and the parts of the two figures which are identical in function, are designated alike.

It will be observed that in Fig. 2, instead of employing .a single harmonic voltage developing resistor for all the slat electrodes, each slat electrode 4 is connected to the positive terminal I3 through an individual resistor ||a, lll), etc. These resistors are connected to the respective filters 34, 35, etc., which in turn are connected to the harmonic stop selector 53, and thence through the mixer 40 and the amplifier 3|, as above described in connection with Fig. l, it being understood, of course, that the amplifier 3| is also supplied with the fundamental note frequencies over the conductors 29, 30, as above described. One of the additional advantages for the arrangement of Fig. 2, is that when using a single harmonic voltage developing resistor as in Fig. 1, it may be impractical to provide each of the filters with the proper range and characteristics for all of the frequencies generated in the tube. For example, suppose that, the lowest note generated by the tube were middle C (250 cyclesper former foreach section having a primary Winding coupled for regenerative feedbackaction be.; tween the grid and anode, means to tune each transformer to a different audio frequency, an audio frequency amplifier and sound transducer combination, means to connect the secondaries of all said transformers in series to the input of said amplifier, a keyboard having a series of keys one for each tube section for controlling the regenerative action in each of said tube sections and means connected in common to all the slat electrodes to selectively apply to said transducer any desired harmonics of the audio frequency wave.

3. VAn electronic organ, comprising, an electronv tube having a central electron-emitting cathode, a cage electrode immediately surrounding said cathode, said cage electrode having a series of conductive slat members defining thereloem tween electron `windows, a plurality of control grids surrounding said cage and each located in registry with one of said windows, a plurality of anodes surrounding said control grids and also in registry with said windows, an audio frequency feedback circuit connecting each anode to each grid to generate discrete audio frequency oscillations, means to tune each feed.4

back circuit to a different audio frequency, a source of common anode potential for all said anodes, a keyboard having a plurality of keys one for each of said feedback circuits for individually controlling the application of anode potential to any of said anodes and means connected in common to said slat members to selec,- tively apply to said transducer any desired harmonics of the audio frequency wave.

4. An electronic organ, comprising, an electron tube having a central electron-emitting cathode, a conductive cage immediately surrounding said cathode and comprising a plurality of spaced conductive slats each pair of slats defining an electron permeable Window, a plurality of grids surrounding said slats each in registry with one of said windows, a plurality of anodes surrounding said grids and also in registry with said windows, a tuned audio frequency feedback circuit connecting each grid to its anode, a key board having a plurality of keys for controlling each of said tuned feedback circuits, and circuit connections for deriving from said Slat electrodes harmonics of the audio frequencies generated in said feedback circuits.

5. An electronic organ, comprising, an electron tube having a central electron-emitting cathode, a cage electrode immediately surrounding said cathode and having a plurality of slats defining electron permeable Windows, said cage electrode having means to subdivide the space around said cathode intoa series of discrete electron chambers with a window in each chamber facing said cathode, a separate control grid and anode located in each chamber, an audio frequency transformer having a primary winding connecting each grid to its associated anode for feedback action, a common source of direct current potential for all said anodes, a keyboard having an individual key for each anode for controlling the application of anode potential thereto, means to tune each transformer primary winding to a separate fundamental audio frequency, an .audio frequency amplifier, means connecting all the secondary windings of said transformers in series across the input of said amplifier, a loudspeaker` connected to the output of said amplifier, means connecting circuit, means connected in'common to said slat said cage electrode through a load resistor to a sourceof direct current to derive across said resistor voltage Waves which are harmonically related tosaid fundamental audio frequency waves, and means to mix said harmonic waves with said fundamental waves to produce at the output of said amplifier any desired harmonic content.

6. An electronic organ, comprising, an electron tube having a central electron-emitting cathode, a 'slatted -screen electrode immediately surrounding said cathode with each pair of adjacent slats` defining an electron permeable window, a plurality of grids and anodes surrounding saidcathode and respectively in registryv with said Windows, a vplurality of tuned audio frequency feedback circuits one for each grid and anode, means to tune each feedback circuit to a different fundamental frequency, a common source of directcurrent potential for said anodes, a keyboard having a separate key connecting said source to the electrical midpoint of each of said transformers, resistor means connecting the slats of said slatted electrode to said source, and means to select from said resistor voltage waves which are harmonically related to said fundamental frequencies.

7. An electronic organ according to claim 6, in which all ofl said slats are interconnected to form a single cage electrode, and' said resistor means comprises 'a single resistor for connecting said cage electrode to'said source.

8. An electronic organ according to claim 6, in which each of said slats is individually connected through a separate resistor means to said source, and means are provided for selecting from each o f said individual resistor means any desired harmonic of said fundamental frequency.

9. An electronic organ according to claim 6, in which'the last-mentioned means includes an additional series of stop switches for selectively connecting said resistor means to a common audio frequency amplifier.

10. An electronic organ according to claim 6, in which a common audio frequency amplifier is providedl for said audio frequencies and said harmonies; and the means for selecting said harmonies comprises a plurality of harmonic stop control keys for deriving from said resistor means correspondingrharmonics of said fundamental frequencies, said stop control keys being connected through respective electrical filters to said amplifier.

11. An electronic organ according to claim 2, in which each of said feedback circuits is connected to a commonsource of tremolo potential for imparting a tremolo effect to said fundamental frequency.

12. An electronic organ according to claim 3, in which said source of anode potential is con# nected through a time-constant circuit to smooth the percussive effect of the generated audio frequencies.

13. An electronic organ comprising an evacuated envelope containing a central electronemitting cathode,` a plurality of separate anodes concentrically1 mounted around Ysaid cathode, a pluralityof slatI electrode elements concentrically vn icunted around the cathode and each located between the cathode and the respective anode,- a plurality of tuned oscillatory circuits each connected between said anode and cathode for generating sustained oscillations of respective fundamental audio frequencies, a keyboard having a plurality of keys on'e for each tuned ALBERT M. SKELLETT.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS o Number Name Date 1,782,542 Miller Nov. 25, 1930 1,832,402 Langer Nov. 1'7, 1931 2,126,464 Hammond Aug. 9, 1938 10 2,340,001 McKellip Jan. 25, 1944 2,433,403 Skellett Dec. 30, 1947 FOREIGN PATENTS Number Country Date 293,991 Italy July 19, 1930 

